1. Field of the Invention
The present invention relates to biological treatment of contaminated liquids and effluent, and more particularly to methods and apparatus for the creation and/or application of customized biology populations to biological processes such as wastewater treatment.
2. Description of the Related Art
Before being discharged to the environment, contaminated waters from municipal, commercial and industrial sources frequently must be treated to prevent harmful impacts. The treatment processes used are numerous and varied. A rudimentary conventional process is shown in FIG. 1. The treatment process will often begin with a coarse removal step 10, typically involving screening and grit removal. This may be followed by removal of sludge and solids in a primary clarifier 112. Frequently the sludge from the primary clarifier 112 is partially consumed in a digester 114, which recycles clear effluent back to the start of the process and diverts the unconsumed sludge to disposal.
The clear effluent from the primary clarifier 112 may be mixed with activated sludge and aerated in an aeration unit 118 before being fed to a secondary clarifier 120 for secondary treatment. The clear effluent overflowing the secondary clarifier 120 may be disinfected by a disinfecting unit 122 (which may apply, for example, chlorine or UV light), and discharged to a local waterway as effluent. The solids from the secondary clarifier 120 are generally thickened, e.g., by a filter press 124 and then sent off for disposal.
Biological processes are commonly used for the elimination of contaminants in the secondary treatment portion of the process, and may take many forms. They generally involve exposure of the waste stream to one or more forms of microorganisms that stabilize or digest various contaminants. The microorganisms to be favored by the particular treatment process implemented are chosen to complement the waste stream in terms of content, strength, the biochemical and chemical environment used for treatment, and the specific effluent requirements. For example, the activated sludge process utilizes aerobic bacteria that remove the soluble biological oxygen demand (BOD) from wastewater. Practice of this process generally involves conducting wastewater into an aeration basin containing a suspension of digestive microorganisms, thereby forming a xe2x80x9cmixed liquorxe2x80x9d that is aerated to furnish oxygen for consumption of the BOD, the formation of new biomass, and the respiration of biomass maintained in inventory; the biomass sorbs, assimilates and metabolizes the BOD of the wastewater. After a suitable period of aeration, the mixed liquor is introduced into the secondary clarifier 120 in which the biomass settles, allowing the treated wastewater to overflow into an outlet effluent stream. All or a portion of the biomass separated from the effluent in 120 is returned to 118 to treat additional influent.
The BOD provided by the waste acts as xe2x80x9cfoodxe2x80x9d for the microorganisms. The BOD may be measured and reported as total BOD that includes both nitrogenous (NBOD) and carbonaceous oxygen demand (cBOD) or separately as NBOD and cBOD. This BOD, especially the cBOD, may be present in particulate or soluble form. The propensity of a given organism to metabolize a particular form of NBOD or cBOD and the rate at which this is done are determined by both the local environmental conditions and the number of organisms of similar type. In addition to carbonaceous xe2x80x9cfood,xe2x80x9d microorganisms require certain macronutrients for survival, such as sodium, calcium, phosphorus, and/or nitrogen, and trace levels of micronutrients such as iron, sulfur, and/or manganese. Controlled and efficient removal of these macro and micronutrients from the waste stream by the treatment process may be an important component of its operation with respect to meeting local effluent disposal requirements. As these various materials are metabolized by the microorganisms they may reproduce, and the degradable portions of the influent are converted into gases and excess biology. The excess biology may consist of live and/or expired microorganisms and other organic materials, and will generally be disposed of as sludge at the terminal portion of the process. The clear effluent that remains is generally discharged to a local receiving water body.
The microorganisms selected for the elimination of the contaminants in the incoming waste stream may come from many sources. Most waste treatment processes treat their incoming waste with recycled biology populations obtained from a downstream portion of the process. Recycling of these microorganisms is convenient and inexpensive, but unfortunately does not readily lend itself to the customized matching or tailoring of a given biological population to the varying needs of the influent waste stream. The composition, effectiveness, and amounts of the various recycled populations of microorganisms are also affected by the feed composition present when they were generated, so they are especially impacted by changes in the flow compositions or influent concentrations. These problems are exacerbated by the limited amount of flexibility most treatment plants have in manipulating the factors that favor a desired biological population profile. The options frequently are limited to the wasting of a portion of the sludge or some of its associated water chemistry, in an attempt to drive the biological selection process to a particular population balance by controlling the average xe2x80x9cagexe2x80x9d of the population, balancing the slower growing, more efficient organisms with the faster growing, more responsive organisms.
Partially in response to this need for varied populations, in response to local effluent requirements, and in an effort to accelerate the treatment process, a waste treatment plant may treat the waste stream with a combination of biological environments generally within the secondary treatment portion of the process. While virtually all treatment schemes utilize several major classes of bacteria, including obligate aerobes, facultative aerobes, nitrifiers, obligate anaerobes, and facultative anaerobes, manipulation of the different environments within the particular scheme favor different classes of bacteria must compete with each other in the course of the treatment process. The results of this competition affect and effect the efficiency of the treatment process and the degree of treatment achieved in the final effluent.
Common to all of these processes, however, is generation of a waste stream of excess biology, generated because new growth is in excess of death and decay. In most instances that waste stream also will contain particulate, non-degradable organic and inorganic material in addition to the excess biology. Usually, the waste stream is removed as a portion of a solids recycle stream and it is directed to a terminal solids treatment process, thus minimizing the volume of excess waste solids that must be disposed of. The terminal treatment process functions primarily to concentrate and stabilize these materials for disposal and may include further biological treatment (xe2x80x9cdigestionxe2x80x9d) that specifically enhances general death and decay of biomass.
Both as described and as is generally practiced, the current waste treatment processes exhibit significant limitations. Conventional modes of operation do not allow microorganism populations to be tailored to the characteristics of a particular waste stream, which may change over time. Moreover, although minimizing the quantity of disposable solids is important to the performance of waste treatment systems, the ability to achieve low solids levels is impeded by the problems of excess biology and limited digestion, resulting in excessive operating costs, disposal costs, and potentially adverse environmental impacts.
The preceding problems are addressed by the generation and introduction of specific biology populations that are customized to perform or favor specific tasks either during the main waste treatment process, or for solids minimization purposes in a post-treatment process. These bacteria may be grown from specialized mixes of activated sludge and waste influent by exposing these materials to controlled growing environments (e.g., in an offline treatment area). They may then be added back to the main process to perform certain tasks such as converting particulate cBOD into soluble cBOD for utilization, reducing high solids yield organisms, improving nitrification/denitrification efficiency, or competitively suppressing filamentous biology such as Norcardia sp. Alternatively, the biological population generated may be customized to consume the generated solids residue in order to reduce the overall disposal volumes and costs.
In one aspect the invention provides for the treatment of a waste stream using a growth method that involves mixing a portion of the stream with activated sludge and then using controlled mixing, air exposure, residence time and settling sequences to create specialized population profiles. These specialized biological populations have characteristics that are useful for achieving particular desired results when treating the incoming waste, oftentimes in combination with (or as a pre-existing component of) the main treatment process.
Proper sequencing of growth conditions can, for example, generate a biological population that exhibits a lower solids yieldxe2x80x94that is, the biology converts a higher proportion of the waste to gas than to solids, thereby reducing the volume of solids that must be disposed ofxe2x80x94and enhanced influent waste consumption efficiency. Higher proportions of facultative aerobes or facultative anaerobes can be grown by manipulation of conditions, as can populations with a higher content of nitrifiers. Filamentous biology such as Norcardia sp. can be discouraged, and enhanced levels of nutrients, cBOD, and nitrates can be developed for beneficial introduction into the main treatment process. Accordingly, biology customization can be targeted toward, for example, increasing the concentration of disposable solids at the expense of the biology itself, or reducing the nutrient content of the disposable solids.
Desired growth conditions may be achieved by effecting a selected order of aerobic, anoxic, and anaerobic conditions for varied lengths of time and repetitively controlling those conditions by measurement and reproduction of the oxidation-reduction potential (ORP), specific oxygen uptake rate (SOUR), and/or specific nitrogen uptake rate (SNUR). It should be stressed that these measurements do not represent ends in themselves; obtaining a target level ORP level, for example, will not generally suffice to achieve the objectives of the invention. Instead, such measurements are used as indicators of biological population in the context of a timing regimen, facilitating both control over and awareness of the changing process conditions so that the regimen can be effectively executed.
In one embodiment, a biological population that favors the conversion of particulate cBOD to soluble cBOD for utilization in the main process flow is generated by combining a portion of the incoming waste stream with activated sludge, mixing to achieve anaerobic conditions, allowing the material to settle and then decanting off a portion (e.g., one quarter) of the volume as high-load (high cBOD content) liquor back to the main treatment process to treat an intermediate high nitrate stream generated from the incoming waste. The decanted volume of the off-line process is then replaced with more waste stream material, desirably establishing the suspended solids content within a particular range, and the whole process then repeated. When the suspended solids content of the off-line process mixture eventually becomes too high for effective control of local conditions and mixing, a portion (e.g., half or a third) of the mixture may be removed either to the main process flow or to disposal, after which the process is repeated from the beginning; that portion of enhanced population not removed effects an accelerated rate of treatment by virtue of having been acclimated to both the conditions and function of the off-line process. This growth selection sequence may be continued indefinitely.
The high-load decant produced in accordance with the embodiment exemplified above is high in soluble cBOD, high in ammonia, and has a low ORP. Breakdown of the particulate cBOD and particulate NBOD into soluble cBOD and ammonia may be accomplished by and in the presence of facultative anaerobes at the expense of obligate aerobes and independent of the nitrifier content.
In another embodiment of the invention a biological population favoring the augmentation of biology low in solids yield may be produced by combining a portion of the incoming waste stream with activated sludge, mixing to achieve anaerobic conditions, mixing with aeration to achieve ORP-positive conditions, mixing without aeration to achieve anaerobic conditions, allowing the material to settle and then decanting off a portion (e.g., a quarter) of the volume as high-load liquor back to the main treatment process to treat the incoming waste. If low-load decant is desired, then an additional step of mixing with aeration is performed before decanting back to the main treatment process. In either case, the decanted volume is then replaced with more influent waste stream material, desirably establishing the suspended solids content within a particular range. The whole process may then be repeated once or twice. After this, a portion (e.g., one third) of the completely mixed contents of the off-line process are removed to the main process flow, after which the process may be repeated from the beginning. This selective growth sequence may be continued indefinitely, the initial exposure of biology to food under anaerobic conditions competitively enhancing the number of facultative anaerobes and facultative aerobes capable of cBOD utilization, and the repetitive sequence maintaining (and further increasing by competition) the numbers of such facultative anaerobes and facultative aerobes. The numerically enhanced population of facultatives returned in the mixed decant produced by this embodiment is useful to selectively produce and augment a biological population which is biologically efficient (low in solids yield per weight of cBOD converted to gases) and which is capable of converting raw influent waste into gases without always being under aerated and/or aerobic conditions.
In yet another embodiment of the invention, high-solids-yield organisms are reduced and nitrification/denitrification capacity is improved. This may be accomplished by combining a portion of the incoming waste stream with activated sludge and mixing initially with aeration to achieve aerobic conditions and low ammonia content. The repetitive process begins with mixing without aeration while adding additional influent waste stream material, mixing with aeration to achieve a positive ORP and a significant dissolved oxygen content, stopping the mixing and aeration, allowing the material to settle and the dissolved oxygen content to dissipate, adding more waste stream material and repeating the aeration sequence, then decanting off a portion (e.g., one quarter) of the volume back to the main treatment process. The above steps may be repeated, after which a portion (e.g., one third) of the off-line mixture remaining is removed to the main process flow.
The latter decanted volume is replaced with more activated sludge, desirably establishing the suspended solids content at not more than 7,500 mg/l by the addition of sufficient influent waste stream material, as needed. The process is preferably repeated from the initial aeration sequence through to the return of an enhance population, and the entire process continued indefinitely. The intermediate decant produced by this embodiment is low in nutrient content and is useful in dilution of high strength influent waste; the resulting biological population returned at the end of each sequence is enhance in low solids-yield organisms (facultative aerobes capable of utilizing nitrate and oxygen as energy sources) and enhanced in its population of nitrifiers. With such and enhanced population regularly returned to the main process flow, the main process will be improved in both nitrification and denitrification rate and efficiency as it will be enhanced in the number of nitrifiers and facultative aerobes.
In still another embodiment, a biological population that disfavors filamentous biology or is severely diminished in the numbers of filamentous organisms is generated by combining a portion of the influent waste stream with activated sludge, mixing to achieve and maintain anaerobic conditions for a period of time, stopping the mixing, mixing again, then mixing and aggressively aerating to achieve a highly positive ORP, allowing the material to settle and then decanting off a volume with the biological population diminished in filamentous organisms back to the main process to treat the incoming waste. This embodiment selects against filamentous organisms by elimination of consistently low food to biomass conditions in which they thrive (by virtue of their high surface area to volume ratio) and by favoring conditions that enhance the population of facultative aerobes and nitrifiers.
A second aspect of the invention provides for the improved terminal treatment of waste solids produced by the waste treatment process as a whole by minimizing the quantity of solids that must be disposed of. Application of one or more of the embodiments to enhance the production and maintenance of low yield organisms in the main process flow allows and provides for a total suspended solids content in the main process flow that has lower biological content and a higher content of non-degraded organic (lint, hair, etc.) and inorganic content. In addition to the reduction of solids amounts (and volume) to be disposed of by virtue of the greater conversion to gases of the influent waste stream, the increased inorganic and non-degraded organic content can be concentrated more easily by various gravity and mechanical means normally employed by those familiar with the art of solids handling. Thus the volume of waste to be disposed of is further reduced.
A third aspect of the invention relates to apparatus for the implementation of the foregoing methods. For example, in one embodiment influent waste stream and activated sludge materials are combined in a treatment vessel, the growth of the desired biological population is controlled for, and a means is provided for drawing off a portion of the generated population and using it in another treatment vessel. A controllable aerator may be provided in the first treatment vessel.